The uses of coherent structure (Dryden Lecture)

The concept of coherent structure in turbulent flow is a revolutionary idea which is being developed by evolutionary means. The main objective of this review is to list some solid achievements, showing what can be done by using the concept of coherent structure that cannot be done without it. The nature of structure is described in terms of some related concepts, including celerity, topology, and the phenomenon of coalescence and splitting of structure. The main emphasis is on the mixing layer, as the one flow whose structure is well enough understood so that technical applications are now being made in problems of mixing and chemistry. An attempt is made to identify some conceptual and experimental obstacles that stand in the way of progress in other technically important flows, particularly the turbulent boundary layer. A few comments are included about the role of structure in numerical simulations and in current work on manipulation and control of turbulent flow. Some recent developments are cited which suggest that the time is nearly right for corresponding advances to occur in turbulence modeling

Flow Structure and Optical Beam Propagation in High Reynolds Number, Gas-Phase Shear Layers and Jets

We report on the structure of the scalar index-of-refraction field generated by turbulent, gas-phase, incompressible and compressible shear-layers and incompressible jets, and on associated beam-propagation aero-optical phenomena. Using simultaneous imaging of the optical-beam distortion and the turbulent-flow index-ofrefraction field, wavefront-phase functions were computed for optical beams emerging from the turbulent region in these free-shear flows, in an aero-optical regime producing weak wavefront distortions. Spatial wavefront-phase behavior is found to be dominated by the large-scale structure of these flows. A simple level-set representation of the index-of-refraction field in high Reynolds number, incompressible shear layers is found to provide a good representation of observed wavefront-phase behavior, indicating that the structure of the unsteady outer boundaries of the turbulent region provides the dominant contributions